It is well known to apply designs to ceramic, glass-ceramic and glass products such as, for example, tableware, bakeware and other dishware to esthetically enhance the appearance of the product. Several methods have been employed for applying designs to such products.
According to one process, ceramic pigments are directly printed on glass and ceramic products by means of traditional printing techniques. According to such printing methods, pigments are baked into the surface of the product. As a result, a permanent printed image is obtained on the product. While this printing technique has met with some degree of success, it requires extensive manual preparation and labor. Moreover, the technique is not amenable to consistent reproduction of colors in large quantities. Among other disadvantages of such direct printing is the inability to maintain the resolution quality or the uniformity of the color printing.
Another known process for printing to ceramic, glass-ceramic and glass products relies on the technique of decal image transference. Typically, pigments are transferred via a transfer agent, such as a paper coated with gum arabic. In decal image transference, pigments can be applied to the transfer agent by various printing techniques. For example, conventional ceramic pigments can be applied to the transfer agent by screen printing, such as via rotary screen printing as illustrated in FIG. 2. However, rotary screen printing onto ceramic, glass-ceramic and glass products is labor intensive. It also requires image reproduction by a plurality of color dispensers, each of which requires precise transfer of the resultant inks to form an image. Moreover, image reproduction using rotary screen printing, as illustrated in FIG. 2, typically requires the addition of heat to set an image transferred to the workpiece. Alternatively, ceramic toner may be used in connection with decal transference instead of the conventional printing pigments or inks. In these instances, the ceramic toner can be applied to the transfer agent by electrostatic or electrophotographic reproduction method. In such a process, the transfer agent is applied to the ceramic or glass article at the desired position and either moistened or heated. The transfer agent is then removed leaving the pigmented image on the article. Following the transfer, the product is fired to fuse the pigment with the product.
While the decal image transference technique has also had some degree of success, it also has certain inherent disadvantages. One disadvantage is that the image must be printed on discrete sheets of the transfer agent that must be manipulated during further processing. Thus, the printing process is inherently less efficient than an otherwise automated process would be. Moreover, because each transfer agent sheet requires separate handling, consistent reproducibility of the image is extremely difficult.
Another process for printing to ceramic and glass products is described in U.S. Pat. Nos. 6,487,386 and 6,745,684 in which electrostatic or electrophotographic methods are used in a process to apply ceramic toner directly to the ceramic or glass product. The processes described in each of these patents also have inherent drawbacks. One particular drawback is the inability to permanently affix the image to a ceramic or glass product at or near ambient temperatures, without application of additional heat. Another of the drawbacks of the processes described in U.S. Pat. Nos. 6,487,386 and 6,745,684 is that they do not provide for an overcoat to retard cadmium release or maximize gloss.
The present invention is provided to solve the problems discussed above and other problems, and to provide advantages and aspects not previously provided. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings.